1. Field of the Invention
This invention relates to concrete foundations particularly useful for the support of tall, heavy and or large towers which may be used to support power lines, street lighting and signals, bridge supports, wind turbines, commercial signs, freeway signs, ski lifts and the like.
2. Description of Related Art in Relation to Present Invention
Various different forms of foundations utilizing some of the general structural and operational features of the instant invention heretofore have been known, such as those disclosed in U.S. Pat. Nos. 2,374,624, 2,706,498, 2,724,261, 3,600,865 and 3,963,056. However, these previously known foundations do not include some of the basic features of the instant invention, and the combination of features incorporated in the instant invention enable a heavy duty foundation with a slenderness ratio of less than 3 to be formed in situ and in a manner not requiring the use of large drilling rigs or pile drivers. The combination comprising the present invention results in a foundation capable of resisting very high upset loads in various types of soils and in a manner independent of the concrete of the foundation experiencing alternating localized compression and tension loading.
U.S. Pat. No. 2,374,624 to P. J. Schwendt discloses a foundation intended for supporting signal masts, supply cases and signals. The foundation consists of pre-cast sections of concrete bolted together. The composite foundation is embedded in soil. The mounting of a tall mast section for signals on this foundation would subject the foundation to some overturning moment, and the Schwendt foundation is only applicable to relatively small structures, inasmuch as it is constructed from pre-cast sections which necessarily impose size limitations on the foundation and therefore the structure supported thereon.
In comparison, the pier foundation of the instant invention is poured-on-site monolithically and is of cylindrical construction with many post-tensioned anchor bolts which maintain the poured portion of the foundation under heavy compression, even during periods when the foundation may be subject to high overturning moment.
U.S. Pat. No. 2,706,498 to M. M. Upson discloses a pre-stressed tubular concrete structure particularly adapted for use as pipe conduits, concrete piles and caissons. The pre-stressed tubular concrete structure is pre-cast in sections and can be assembled end-to-end. Longitudinal reinforcing steel is provided and extends through cavities, is tensioned and grouted tight, therefore pre-stressing helical wire windings which are tensioned providing circumferential pre-stressing. The Upson structure is pre-stressed and not of a size diameter suitable as a foundation for tall support towers or columns subject to high upset moment and would be very difficult to transport to a remote area of use.
In contrast, the foundation of the instant invention is poured on site monolithically and, therefore, in the case of a remote point of use, needs only transportation for the ingredients of concrete, corrugated pipe sections and tension bolts to the construction location and only to the extent necessary to construct the foundation in accordance with the present invention.
U.S. Pat. No. 2,724,261 to E. M. Rensaa discloses a pre-cast column and means for attaching the column to a substantially horizontal supporting surface such as a footing or wall and which is otherwise not suitable for use as a large or tall tower foundation.
U.S. Pat. No. 3,600,865 to Francesco Vanich discloses a single column-borne elevated house unit erected by assembling, on a cast in situ foundation pillar, column sections provided with means for fastening the same together and to the foundation pillar above the pillar and by also fastening to the column sections radially arranged cantilever beams. The assembled parts are fastened together and to the foundation pillar by tendon sections which are first coupled together by joints, and then tensioned and eventually bonded to the concrete of the assembled parts by forcing grout in the clearance fully around the tendon rods.
The Vanich house foundation is supported either on a large diameter pile cast or otherwise forced into the ground or inserted with its base portion into a small diameter pit whose peripheral walls and bottom are coated with a thick layer of preferably reinforced concrete. Sheathed steel rods are placed into the pit which is then filled with concrete. Before the concrete is completely hardened, a light pre-fabricated base is fitted thereon with screw threaded rods extending through the base.
U.S. Pat. No. 3,963,056, to Shibuya et al. discloses piles, poles or like pillars comprising cylindrical pre-stressed concrete tubes or pillar shaped pre-stressed concrete poles with an outer shell of steel pipe. While inclusion of the outer steel pipe as the outer shell increases the compressive strength of the concrete tube or pole by preventing the generation of lateral stress within the concrete tube or pole in a radial direction, the outer steel shell provides little resistance to tension stresses imposed upon the concrete due to swaying or side-to-side movement of tall towers supported on the foundation. In contrast, the pier foundation of the instant invention is post-stressed sufficiently to place the entire vertical extent of the concrete portion of the foundation under compression which considerably exceeds any expected tension loading thereof.
Finally, U.S. Pat. No. 1,048,993, to C. Meriwether discloses a reinforced concrete caisson which can be sunk in the usual way. Then, if desired, the caisson may be filled with concrete to form a pier. The reinforced concrete caisson is pre-cast into tubular sections of concrete with heavy large-mesh fabric of wire reinforcement and metal rings embedded at the ends for bolting sections together at a bell and spigot joint. Tie-rods extend through the connecting rings on the inside of the reinforced concrete tube to connect the section together. However, the tensioned tie-rods of Meriwether are spaced inward of the inner peripheries of the concrete tubes and do not pass through the thick wall concrete construction itself.